Elevator safety arrangement having earth fault detection

ABSTRACT

A safety arrangement of an elevator and a method for monitoring electrical safety in an elevator system is disclosed. The safety arrangement of an elevator includes a motor drive of the elevator, which motor drive includes a main circuit, an accessible conducting part, which is earthed, an insulator, which is adapted to electrically insulate the aforementioned conducting part from the aforementioned main circuit and also a monitoring circuit, which is configured to determine an earth fault of the aforementioned main circuit occurring via the aforementioned conducting part. The monitoring circuit is configured to form a signal indicating the danger of electric shock in the motor drive of the elevator, if the aforementioned earth fault is diagnosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of copending U.S. application Ser.No. 14/678,111, filed on Apr. 3, 2015, which is a Continuation of PCTInternational Application No. PCT/FI2013/051037, filed on Nov. 1, 2013,which claims priority under 35 U.S.C. 119(a) to Patent Application No.20126150, filed in Finland on Nov. 5, 2012, all of which are herebyexpressly incorporated by reference into the present application.

FIELD OF THE INVENTION

The invention relates to solutions for monitoring the electrical safetyof motor drives and particularly the electrical safety of the motordrives of an elevator or conveyor.

BACKGROUND OF THE INVENTION

The requirements for protection of a motor drive against electric shockare presented e.g. in the standards IEC 61140: “Protection againstelectric shock. Common aspects for installation and equipment.”; IEC60364-4-41: “Low-voltage electrical installations—Part 4-41: Protectionfor safety—Protection against electric shock”; IEC 60204-1: “Electricalequipment of machine”; IEC 61800-5-1: “Adjustable Speed electrical powerdrive systems—Part 5-1: Safety requirements—Electrical, thermal andenergy”.

According to standard EN 61140 a fundamental rule of protection againstelectric shock is that hazardous-live parts shall not be accessible andthat accessible conductive parts shall not be hazardous live in normalcircumstances or as a consequence of a single fault. For these reasonsaccessible conducting parts are normally earthed.

AIM OF THE INVENTION

One aim of the invention is to improve the protection of elevatorsagainst electric shock. To achieve this aim the invention discloses asafety arrangement of an elevator according to claim 1, and an elevatorsystem according to claim 15.

One aim of the invention is to improve the protection of conveyorsagainst electric shock. To achieve this aim the invention discloses asafety arrangement of a conveyor according to claim 14.

One aim of the invention is to improve the protection of a frequencyconverter, and also of an electric motor to be connected to a frequencyconverter, against electric shock. To achieve this aim the inventiondiscloses a frequency converter.

The preferred embodiments of the invention are described in thedependent claims. Some inventive embodiments and also inventivecombinations of the various embodiments are also presented in thedescriptive section and in the drawings of the present application.

SUMMARY OF THE INVENTION

The safety arrangement of an elevator comprises a motor drive of theelevator, which motor drive comprises a main circuit, an accessibleconducting part, which is earthed, and also an insulator, which isadapted to electrically insulate the aforementioned conducting part fromthe aforementioned main circuit. The safety arrangement of an elevatorcomprises a monitoring circuit, which is configured to determine anearth fault of the aforementioned main circuit and, if theaforementioned earth fault is diagnosed, to form a signal indicating thedanger of electric shock in the motor drive of the elevator. In the mostpreferred embodiment of the invention the aforementioned insulator(electrical insulator) is fitted between the aforementioned conductingpart and the aforementioned main circuit. In the invention an earthfault of the main circuit preferably means a situation in which anearthed conducting part comes into electrical contact with a live partof the main circuit as a consequence of an insulation failure. Anaccessible conducting part means a part that can be accessed withoutdisassembling a structure of the motor drive and which for this reasoncan cause an electric shock hazard to people in the proximity of themotor drive. The conducting part can be e.g. a part made wholly orpartly from metal, which conducts electricity owing to, inter alia, thefree charge carriers in it.

The inventors have realized that an insulation fault in the motor driveof an elevator can cause a dangerously high contact voltage inaccessible conducting parts of the motor drive of an elevator, even ifthe aforementioned parts were earthed. This results from, inter alia,the total impedance from a conducting part to earth being so great,owing to the earthing structures used or owing to deficiencies in theearthing structures, that a large contact voltage in an earthedconducting part is possible. In addition, if an earth fault occurs onthe output side of a motor drive the short-circuit protections beingused on the input side of the motor drive do not necessarily detect adangerous situation, because voltage conversion and current conversionoccur in the motor drive. Consequently the current of the output sidecan be considerably greater than the current of the input side; also thelarge impedance of an earthing structure can limit the ground leakagecurrent to below the detection limit. The problem is also cumulative insuch a way that when the impedance of an earthing structure, andconsequently the contact voltage of an earthed conducting part,increases in an earth fault situation, the ground leakage currentdecreases, making detection of a dangerous situation more difficult.

The solution according to the invention enables the protection ofaccessible, earthed conducting parts of a motor drive of an elevatoragainst electric shock, more particularly as a precaution against aninsulation failure occurring in the motor drive.

An insulator (electrical insulator) is fitted to electrically insulate aconducting part of the motor drive of an elevator from the main circuitof the motor drive of the elevator when the use of an insulator isnecessary for achieving sufficient insulation protecting from electricshock, as specified in the electrical safety regulations or elsewhere,between the aforementioned conducting part of the motor drive of theelevator and the aforementioned live main circuit of the motor drive ofthe elevator. The aforementioned conducting part of the motor drive ofan elevator is preferably earthed with earthing means, preferably withan earthing cable, an earthing bar or corresponding. In one preferredembodiment of the invention the aforementioned conducting part isdisposed in the immediate proximity of the main circuit of the motordrive of the elevator. In one preferred embodiment of the invention theaforementioned conducting part mechanically connects to theaforementioned main circuit via the insulator.

The aforementioned earthed conducting part of the motor drive of anelevator can consequently be e.g. a cubicle for electrical devices, orpart thereof, a connector of the main circuit of the motor drive, anenclosure or heatsink of the frequency converter, an enclosure of acontrol device or a user interface in connection with the motor drive,an enclosure of the fan for the power semiconductors of the maincircuit, an enclosure of a fan for the electric motor, an enclosure fora brake control device of the elevator, a mechanical brake for theelevator or a brake part, a frame part of the hoisting machine of theelevator or a terminal box on the motor drive of the elevator. Theconducting part can also be some part outside the motor drive, whichpart is accessible and which connects in an electrically conductivemanner to an earthed conducting part of the motor drive of the elevator.

In one preferred embodiment of the invention the monitoring circuit isconfigured to determine an earth fault of the aforementioned maincircuit from the ground leakage current of the aforementioned conductingpart. In the invention the ground leakage current of a conducting partof the motor drive of an elevator means the current that flows from thelive main circuit of the motor drive via the aforementioned conductingpart to earth.

In one preferred embodiment of the invention the monitoring circuit isconfigured to form a signal indicating failure of the aforementionedinsulator on the basis of a diagnosed earth fault of the aforementionedmain circuit.

In one preferred embodiment of the invention the safety arrangement isfunctional for forming a signal indicating the danger of electric shockin the motor drive, both when driving with the elevator and during astandstill of the elevator. Consequently the signal indicating thedanger of electric shock can be formed as quickly as possible when adangerous situation occurs, in which case the elevator can be removedfrom use without it causing a hazard to elevator passengers or toelevator servicing personnel. Servicing personnel can also be informedabout the danger of electric shock and corrective actions can in thiscase be started as quickly as possible after the appearance of thedangerous situation.

In one preferred embodiment of the invention the monitoring circuitcomprises a sensor, which is configured to measure the current flowingin the main circuit of the motor drive of the elevator, and themonitoring circuit is configured to determine the ground leakage currentof a conducting part of the aforementioned motor drive of the elevatorby means of the current measurement data to be received from the sensor.In a preferred embodiment of the invention a sensor belonging to thecontrol apparatus of the hoisting machine of the elevator is used as asensor, in which case the number of sensors needed in the motor drivebecomes less.

In one preferred embodiment of the invention the monitoring circuitcomprises a processor and also a memory, in which a program to beexecuted by the processor is recorded, and a determination method fordetermining an earth fault of the aforementioned main circuit isrecorded in the aforementioned memory.

In one preferred embodiment of the invention the safety arrangementcomprises a control circuit in connection with the monitoring circuitfor resolving the operating state of the elevator.

In one preferred embodiment of the invention at least two differentdetermination methods for determining an earth fault of the main circuitare recorded in the memory, and the monitoring circuit is configured toselect the earth fault determination method to be used at any given timeon the basis of the resolved operating state of the elevator.

In one preferred embodiment of the invention the monitoring circuit isconfigured to use a different determination method when driving with theelevator than during a standstill of the elevator for determining anearth fault.

In one preferred embodiment of the invention the monitoring circuitcomprises a memory, in which the threshold value of the ground leakagecurrent of the conducting part is recorded, and the monitoring circuitis configured to diagnose an earth fault in the main circuit when theground leakage current of the conducting part exceeds the thresholdvalue. In this case the threshold value of the ground leakage currentcan be selected to be suitable for detecting an electric shock hazard inthe conducting part.

In one preferred embodiment of the invention the aforementionedthreshold value of a ground leakage current is determined in an earthfault situation from the magnitude of the current flowing via theearthing means of the conducting part of the motor drive of theelevator. In this case the threshold value of the ground leakage currentcan be selected to be sufficiently small, taking the impedance of theearthing means against earth into account, to prevent dangerous (>50volts) contact voltage in an earthed conducting part. In this way theproblem relating to the simultaneous dangerous contact voltage and lowground leakage current, which hampers detection of an earth fault,resulting from the impedance of an earthing structure in an earth faultsituation can be solved.

In one preferred embodiment of the invention the monitoring circuit isconfigured to select the threshold value of the ground leakage currentof the conducting part on the basis of the resolved operating state ofthe elevator. In this case the threshold value of the ground leakagecurrent can be smaller during a standstill of the elevator than whendriving with the elevator, because during a standstill of the elevatoralso the interference level of the main circuit of the motor drive issmaller, which improves the measurement accuracy/determination accuracyof the ground leakage current.

In one preferred embodiment of the invention the main circuit of themotor drive of the elevator is formed from at least two subcircuits, andthe motor drive of the elevator comprises one or more insulators, whichis/are adapted to electrically insulate one or more of theaforementioned subcircuits from the earthed conducting part of the motordrive of the elevator. In this case the monitoring circuit can beconfigured to specify the subcircuit in which an earth fault hasoccurred. The signal formed by the monitoring circuit indicating adanger of electric shock in the motor drive can also contain moreprecise information, based on the aforementioned specification, as towhich part of the motor drive of the elevator the danger of electricshock applies.

In one preferred embodiment of the invention one or more of theaforementioned subcircuits to be electrically insulated with aninsulator from a conducting part of the motor drive is/are connected toat least one second subcircuit with one or more controllable electronicswitches, the control pole of which switch(es) is connected to amonitoring circuit. The monitoring circuit is configured by connectingthe aforementioned electronic switch/electronic switches to determine anearth fault of a subcircuit to be electrically insulated from theaforementioned conducting part occurring via an earthed conducting partof the motor drive. In this case an earth fault of a conducting part canbe determined in a part of the circuit situated in the immediateproximity of the conducting part, in which case the accuracy andreliability of the determination of ground leakage current improve. AnIGBT transistor, MOSFET transistor, thyristor, bipolar transistor,silicon-carbide (SiC) MOSFET transistor or corresponding controllablesolid-state switch can be used as an electronic switch.

In one preferred embodiment of the invention disconnection means arefitted in connection with the monitoring circuit for disconnecting thecurrent in the main circuit of the motor drive of the elevator, and themonitoring circuit is configured to disconnect the current in the maincircuit when an earth fault is diagnosed. In this case the electricalsafety of the motor drive can be ensured by de-energizing the conductingpart that possesses an electric shock hazard by disconnecting thecurrent of the conducting part immediately after an earth fault has beendetected.

In one preferred embodiment of the invention the monitoring circuit isconfigured to disconnect the current in a subcircuit of the main circuitby opening the electronic switch connecting the subcircuit, that is tobe electrically insulated from the conducting part of the motor drive,to the second subcircuit. In this case the conducting part thatpossesses an electric shock hazard can be de-energized by disconnectingthe current from only a part of the main circuit of the motor drive, inwhich case the electricity supply to the electrical devices of theelevator (lighting, air-conditioning, displays, elevator control unit,et cetera) via a live part of the main circuit is still possible.

In one preferred embodiment of the invention the main circuit comprisestwo subcircuits, and the motor drive of the elevator comprises one ormore insulators, which is/are adapted to electrically insulate the firstof these subcircuits from the first earthed conducting part in the motordrive of the elevator and the second of these subcircuits from thesecond earthed conducting part in the motor drive of the elevator. Themonitoring circuit comprises at least two sensors, the first of which isconfigured to measure the current flowing in the aforementioned firstsubcircuit and the second is configured to measure the current flowingin the aforementioned second subcircuit. The monitoring circuit isconfigured to determine the ground leakage current of the aforementionedfirst conducting part by means of the current measurement data to bereceived from the first sensor, and the monitoring circuit is configuredto determine the ground leakage current of the aforementioned secondconducting part by means of the current measurement data to be receivedfrom the second sensor. In this case the monitoring arrangement can beconfigured to specify the conducting part of the motor drive of theelevator, said conducting part being electrically insulated from thesubcircuit/subcircuits and in which part ground leakage current flows,and the signal formed by the monitoring circuit indicating a danger ofelectric shock in the motor drive can also in this case contain moreprecise information, based on the aforementioned specification, as towhich part of the motor drive of the elevator the danger of electricshock applies. In addition, the accuracy of current measurement andconsequently the determination accuracy of a ground leakage current of aconducting structure of the elevator improve when the sensor is situatedcloser to the conducting structure having the ground leakage currentbeing determined.

In one preferred embodiment of the invention the motor drive of theelevator comprises an electric motor and also a frequency converter,with which the electric motor is controlled. The frequency convertercomprises a network bridge to be connected to a power source, a motorbridge to be connected to an electric motor, and also a direct-currentintermediate circuit connecting the network bridge and the motor bridge.

In one preferred embodiment of the invention the motor bridge comprisescontrollable electronic switches for supplying electric power from thedirect-current intermediate circuit to the electric motor, when drivingwith the electric motor, and also from the electric motor to thedirect-current intermediate circuit, when braking with the electricmotor. The motor drive also comprises an insulator, which is adapted toelectrically insulate an earthed conducting part of the motor drive ofthe elevator from the output circuit of the frequency converter, whichoutput circuit is formed from a subcircuit, of the main circuit of themotor drive, continuing from the motor bridge to the electric motor. Themonitoring circuit is configured to determine an earth fault of theoutput circuit of the frequency converter by connecting the electronicswitches of the motor bridge with a switching instruction according tothe determination method. Consequently an earth fault occurring from theoutput circuit via a conducting part can be determined accurately andnear the conducting part using the controllable electronic switches thatare in the motor bridge of the frequency converter.

In one preferred embodiment of the invention the aforementioned sensoris configured to measure the current flowing in the aforementionedoutput circuit of the frequency converter, and the monitoring circuit isconfigured to determine the ground leakage current of an earthedconducting part to be electrically insulated with an insulator from theoutput circuit of the frequency converter from those values for currentwhich the current measured from the output circuit of the frequencyconverter receives when connecting the electronic switches of the motorbridge with a switching instruction according to the currentdetermination method.

In one preferred embodiment of the invention the monitoring circuit isconfigured, when diagnosing an earth fault in the output circuit, todisconnect with the aforementioned controllable electronic switches ofthe motor bridge the electricity supply in the output circuit of thefrequency converter. In this case the conducting part can bede-energized by disconnecting the current only in the output circuit ofthe frequency converter, in which case the electricity supply to theelectrical devices of the elevator (lighting, air-conditioning,displays, elevator control unit, et cetera) is still possible via a livepart of the main circuit, such as via a direct-current intermediatecircuit. In addition, the ground leakage current can be disconnected andthe conducting part that possesses an electric shock hazard can bede-energized using the controllable electronic switches that are in themotor bridge.

In one preferred embodiment of the invention the motor drive of theelevator comprises an insulator, which is adapted to electricallyinsulate an earthed conducting part of the motor drive from the internalcircuit of the frequency converter, which internal circuit is formedfrom a subcircuit of the main circuit of the motor drive, continuingfrom the motor bridge via the direct-current intermediate circuit andnetwork bridge to the supply conductors of the power source. Themonitoring circuit is configured to determine an earth fault of theinternal circuit of the frequency converter, and the monitoring circuitis configured when it diagnoses an earth fault in the internal circuitto disconnect the electricity supply from the power source to theinternal circuit of the frequency converter. Consequently an earth faultoccurring from the internal circuit via a conducting part can bedetermined accurately and near the conducting part. In addition, theconducting part causing an electric shock hazard can be de-energized bydisconnecting the current in the internal circuit of the frequencyconverter. In addition, when the current in the internal circuit of thefrequency converter is disconnected, the current flow in the maincircuit of the frequency converter disconnects and the danger ofelectric shock is removed.

In one preferred embodiment of the invention the aforementioned sensoris configured to measure the current flowing in the aforementionedinternal circuit of the frequency converter, and the monitoring circuitis configured to determine the ground leakage current of the conductingpart to be electrically insulated with an insulator from the internalcircuit of the aforementioned frequency converter from the currentflowing in the internal circuit. The monitoring circuit is configured todisconnect the electricity supply from the power source to the internalcircuit when the ground leakage current of the aforementioned conductingpart to be electrically insulated from the internal circuit exceeds athreshold value.

In one preferred embodiment of the invention the safety arrangementcomprises a contactor, which is fitted in series between the powersource and the internal circuit of the frequency converter, themonitoring circuit is configured to disconnect the electricity supplyfrom the power source to the internal circuit by controlling thecontacts of the contactor open. In this case the conducting part thatpossesses an electric shock hazard can be de-energized with thecontactor.

In one preferred embodiment of the invention the network bridgecomprises controllable electronic switches for supplying electric powerbetween the power source and the direct-current intermediate circuit,and the safety arrangement comprises a short-circuit protective device,which is fitted in series between the power source and the networkbridge. The monitoring circuit is configured to disconnect theelectricity supply from the power source to the internal circuit bytripping the short-circuit protective device by controlling theelectronic switches in the different phases of the network bridge to besimultaneously conductive. In this case the conducting part causing anelectric shock hazard can be de-energized by tripping the short-circuitprotective device, in which case the current from the power source tothe internal circuit of the frequency converter is disconnected. Thesolution is consequently suited for use also in systems in which thefrequency controller is implemented without a single mechanicalcontactor.

In one preferred embodiment of the invention the monitoring circuitcomprises a power meter for measuring the power entering the maincircuit of the motor drive and also the power leaving the main circuit,and the monitoring circuit is configured to determine an earth fault ofthe main circuit of the motor drive of the elevator occurring via anearthed conducting part of the motor drive of the elevator from thedifference between the power coming into the main circuit and the powerleaving the main circuit. In the most preferred embodiment of theinvention the monitoring circuit is configured to form a signalindicating the danger of electric shock in the motor drive, if the powerP_(out) leaving the main circuit is greater by the amount of thepredetermined threshold value s than the power P_(in) coming into themain circuit times the internal efficiency ratio η of the main circuit:P _(out) −P _(in) *η≥s.

By using a measurement of power in the determination of ground leakagecurrent instead of just a measurement of current, the accuracy of thedetermination of ground leakage current can be improved because, unlikein the measuring of current, in the measuring of power the correctmeasurement result is obtained regardless of the current/voltageconversion occurring in the main circuit.

The invention also relates to a safety arrangement of a conveyor, whichsafety arrangement comprises a motor drive of the conveyor, which motordrive comprises a main circuit, an accessible conducting part, which isearthed, and also an insulator, which is adapted to electricallyinsulate the aforementioned conducting part from the aforementioned maincircuit. The safety arrangement of a conveyor comprises a monitoringcircuit, which is configured to determine an earth fault of theaforementioned main circuit and, if the aforementioned earth fault isdiagnosed, to form a signal indicating the danger of electric shock inthe motor drive of the conveyor. The aforementioned conveyor ispreferably a travelator or an escalator.

The solution according to the invention enables the protection ofaccessible, earthed, conducting parts of the motor drive of a conveyoragainst electric shock, more particularly as a precaution against aninsulation failure occurring in the motor drive.

The invention also relates to an elevator system, which comprises amotor drive for driving an elevator car. The elevator system alsocomprises a safety arrangement according to the description, formonitoring the electrical safety of the elevator.

In one preferred embodiment of the invention the safety arrangementcomprises a drive prevention apparatus connected to the monitoringcircuit, which apparatus is configured to remove the elevator from usewhen an earth fault is diagnosed. In this case use of the elevator canbe prevented when the electrical safety of the motor drive is impaired.

In one preferred embodiment of the invention the elevator system isequipped to send a signal indicating the danger of electric shock in themotor drive to a servicing center via a remote connection. In this caseimpairment of electrical safety and an electric shock hazard can bebrought to the attention of the service personnel of the elevators assoon as possible after detecting the hazard, and also corrective actionsand measures ensuring safety can be started as soon as possible.

The frequency converter according to the invention for driving anelectric motor comprises an earthed conducting part and also a maincircuit, which comprises a network bridge, a direct-current intermediatecircuit, a motor bridge, a connection for the electric motor of thehoisting machine and also a connection for a power source. The frequencyconverter also comprises an insulator, which is adapted to electricallyinsulate the aforementioned conducting part to be earthed from theaforementioned main circuit. The frequency converter further comprises amonitoring circuit, which is configured to determine an earth fault ofthe main circuit occurring via the aforementioned conducting part to beearthed and, when the aforementioned earth fault is diagnosed, to form asignal indicating the danger of electric shock. The frequency converteraccording to the invention enables the protection from electric shock ofaccessible, earthed, conducting parts in the frequency converter as wellas in the immediate proximity of the main circuit of the frequencyconverter, e.g. as a precaution against an insulation failure.

In one preferred embodiment of the invention the monitoring circuit isconfigured to determine the ground leakage current of the conductingpart to be earthed. The monitoring circuit comprises a memory forrecording a threshold value for ground leakage current, and themonitoring circuit is configured to diagnose an earth fault when thedetermined ground leakage current of the aforementioned conducting partto be earthed exceeds the aforementioned threshold value for groundleakage current.

In one preferred embodiment of the invention the monitoring circuitcomprises a processor and also a memory, in which a program to beexecuted by the processor is recorded. A determination method fordetermining an earth fault of the main circuit occurring via theaforementioned conducting part to be earthed is recorded in theaforementioned memory.

In the method according to the invention for monitoring electricalsafety in an elevator system an accessible conducting part of the motordrive of the elevator is earthed with earthing means, the aforementionedearthed conducting part is electrically insulated from the main circuitof the motor drive of the elevator with an insulator, an earth fault ofthe main circuit occurring via the aforementioned earthed conductingpart is determined, and, if the aforementioned earth fault is diagnosed,a signal indicating the danger of electric shock in the motor drive isformed.

In one preferred embodiment of the invention a ground leakage current ofthe aforementioned earthed conducting part is determined, and also anearth fault of the main circuit occurring via the aforementioned earthedconducting part is diagnosed, when the determined earth fault currentexceeds the threshold value for the current.

In one preferred embodiment of the invention the operating state of theelevator is determined and also an earth fault of the main circuitoccurring via the aforementioned conducting part is determined using afirst determination method when driving with the elevator, and an earthfault of the main circuit occurring via the aforementioned conductingpart is determined using a second determination method during astandstill of the elevator, said second method differing from the firstmethod.

In one preferred embodiment of the invention the electronic switches ofthe motor bridge of the frequency converter of the motor drive of anelevator are connected with a switching instruction according to thecurrent determination method, the current of the frequency converter isdetermined and also the ground leakage current of the aforementionedconducting part is determined from those values for current which thecurrent of the frequency converter receives when connecting theelectronic switches of the motor bridge with a switching instructionaccording to the current determination method.

In one preferred embodiment of the invention the current in the maincircuit of the motor drive of the elevator is disconnected when an earthfault is diagnosed in the main circuit.

In one preferred embodiment of the invention the electronic switches areconnected in the different phases of the network bridge of the frequencyconverter of the motor drive of the elevator to be simultaneouslyconducting when an earth fault of the main circuit is diagnosed.

As an addition to the invention presented above, or alternatively as awholly separate invention, an apparatus and a method are also disclosedfor disconnecting the power supply of the motor drive of an elevator.The apparatus comprises a frequency converter, which comprises a networkbridge and also a direct-current intermediate circuit. The networkbridge comprises controllable electronic switches for supplying electricpower between the power source of the motor drive and the direct-currentintermediate circuit, and the apparatus comprises a short-circuitprotective device, which is fitted in series between the power sourceand the network bridge. The apparatus also comprises a control circuit,which is configured to receive a control signal and also on the basis ofthe control signal to trip the short-circuit protective device bycontrolling the electronic switches in the different phases of thenetwork bridge to be simultaneously conductive. In this case the motordrive can be de-energized, e.g. in a dangerous situation of theelevator, by tripping the short-circuit protective device on the basisof a control signal indicating the dangerous situation. In the method ashort-circuit protective device is fitted between the power source andthe network bridge of the frequency converter of the motor drive of anelevator, the safety of the elevator is determined and also theelectronic switches are connected in the different phases of the networkbridge to be simultaneously conducting when it is detected that thesafety of the elevator is impaired.

The preceding summary, as well as the additional features and additionaladvantages of the invention presented below, will be better understoodby the aid of the following description of some embodiments, saiddescription not limiting the scope of application of the invention.

BRIEF EXPLANATION OF THE FIGURE

FIG. 1 presents a diagrammatic view of an elevator system according toan embodiment of the invention.

MORE DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 presents a diagrammatic view of a motor drive 1 of an elevator.The motor drive 1 comprises a frequency converter and a hoistingmachine. The elevator car is driven in an elevator hoistway with ahoisting machine via rope friction or belt friction. The speed of theelevator car is adjusted to be according to the target value for thespeed of the elevator car, i.e. the speed reference, calculated by theelevator control unit 8. The speed reference is formed in such a waythat the elevator car can transfer elevator passengers from one floor toanother on the basis of elevator calls given by passengers. In theembodiment of FIG. 1 the elevator system is without machine room, inwhich case the hoisting machine and also the frequency converter aredisposed in the elevator hoistway. However, the invention is also suitedfor use in elevator systems provided with machine rooms.

The elevator car is connected to the counterweight with ropes or with abelt traveling via the traction sheave of the hoisting machine. Variouselevator mechanics solutions known in the art can be used in an elevatorsystem, which do not however clarify the invention and are consequentlynot presented in order to simplify the description.

The hoisting machine comprises an electric motor 7, with which theelevator car is driven by rotating the traction sheave, as well as twoelectromagnet brakes 3C, with which the traction sheave is braked andheld in its position. The hoisting machine is driven by supplyingelectric power with the frequency converter from the supply panel 15 ofthe building to the electric motor 7. The supply panel 15 is situatedoutside the elevator hoistway and consequently in a different locationthan the motor drive 1 of the elevator. The frequency convertercomprises a main circuit 2, which comprises a network bridge 10, withwhich the supply voltage of the alternating electricity network comingfrom the supply panel 15 is rectified into the direct-currentintermediate circuit 11 of the frequency converter. The direct-currentvoltage of the direct-current intermediate circuit 11 is furtherconverted into the variable-amplitude and variable-frequency supplyvoltage of the electric motor 7 by switching the IGBT transistors 14 ofthe motor bridge 12. Adjustment of the speed of the elevator car occurswith the control unit 6 of the frequency converter, which control unitreceives a speed reference from the elevator control unit 8 via a datachannel between the control unit 6 of the frequency converter and theelevator control unit 8. The control unit 6 of the frequency converterreceives measuring data about the speed of rotation of the tractionsheave of the hoisting machine of the elevator and adjusts the speed ofrotation of the traction sheave, and consequently the speed of theelevator car, to be according to the speed reference by adjusting thetorque of the electric motor 7 with the frequency converter. Adjustmentof torque occurs by forming the output voltage of the motor bridge withIGBT transistors 14 by modulating, i.e. by connecting the IGBTtransistors with a suitable switching instruction preferably accordingto pulse width modulation.

During motor braking power returns from the electric motor 7 to thedirect-current intermediate circuit 11 of the frequency converter, inwhich case the voltage of the direct-current intermediate circuit 11starts to rise. The returning power is supplied from the direct-currentintermediate circuit 11 onwards to the electricity network by adjustingthe current of the mains chokes 20 by switching the IGBT transistors 16of the network bridge 10. The voltage of the direct-current intermediatecircuit 11 can be adjusted by means of a chopper circuit formed by thechokes 20 and the IGBT transistors to a set constant voltage higher thanthe network voltage. One constant voltage of a direct-currentintermediate circuit 11 suitable for a European 230-Volt electricitynetwork is approx. 650 Volts, but the voltage can also be higher orlower than this.

The electromagnetic brakes 3C of the hoisting machine are controlled bysupplying current to the electromagnets of the brakes with a brakecontrol circuit 13, which is connected to the direct-currentintermediate circuit 11 of the frequency converter.

In the motor drive of an elevator are accessible parts conductingelectricity, which for safety reason are earthed. Consequently the framepart 3B of the hoisting machine as well as the machinery brakes 3Cattached to the frame part 3B are earthed by fixing an earthing cable 5(a yellow-green cable as per electrical installation instruction) at thepoint of the terminal box 3D of the motor. Also the sheet-metalenclosure 3A of the frequency converter as well as the fan enclosure 3Eare connected to the aforementioned earthing cable 5. The earthing cable5 runs in the same cable bundle as the supply cables coming from thesupply panel 15, and the second end of it is connected to an earthingelectrode 22 in the supply panel 15.

Owing to the high voltage in the main circuit of the frequencyconverter, the live parts of the main circuit are insulated from theaforementioned accessible, electrically-conductive parts 3A, 3B, 3C, 3D,3E of the motor drive with an electrical insulator 4, i.e. with amaterial that conducts electricity badly and is did-electric, i.e.resistant to an external electrical field. A suitable plastic, ceramic,varnish, et cetera, can be used as the insulator 4. The insulation ismade in those points in which the live main circuit 2 is situated soclose to the conducting part 3A, 3B, 3C, 3D, 3E that use of an insulator4 is necessary in order to achieve a sufficient insulation distance. Inthe embodiment of FIG. 1 insulators 4 have been used to insulate thechokes 20 in the frequency converter, the network bridge 10, thedirect-current intermediate circuit 11, the motor bridge 12 and also thebrake controller 13 from the sheet-metal enclosure 3A of the frequencyconverter. In addition, an insulator 4 has been used to insulate thewindings of the motor 7 from the conducting frame 3B of the hoistingmachine.

Damage of an insulator 4 can cause an earth fault, i.e. an electricalconnection of a live part of the main circuit 2 to a conducting part 3A,3B, 3C, 3D, 3E and onwards via the earthing cable 5 of the conductingpart 3A, 3B, 3C, 3D, 3E to earth 22. In the embodiment of FIG. 1 theearthing cable 5 is quite long because the earthing cable is connectedto the earthing electrode only in the supply panel 15, which is disposedat a distance from the motor drive 1. Consequently the impedance 21 ofthe earthing cable 5 is so great that an earth fault causes adangerously high (over 50 Volts) contact voltage in the aforementionedaccessible earthed parts 3A, 3B, 3C, 3D, 3E. The high impedance 21 ofthe earthing cable also limits the ground leakage current flowing in theearthing cable 5, which hampers detection of an earth fault, and e.g.conventional residual current protection in the supply panel 15 is notnecessarily able to detect an earth fault. Detection is also hampered bythe voltage conversion and current conversion occurring in the motordrive, i.e. the current leaving the motor bridge 12 into the motorcables can be considerably larger than the current flowing from thesupply panel 15 to the network bridge 10. The aforementioned voltageconversion and current conversion can be caused by, inter alia, energystorages in the main circuit of the frequency converter, said storagesbeing such as capacitors in the intermediate circuit 11, chokes and alsothe inductance in the windings of the motor, which energy storages canin certain situations supply some of the ground leakage current.

For the aforementioned reasons, among others, a safety arrangement isarranged in the motor drive 1 of the elevator, with which safetyarrangement the electrical safety of the motor drive 1 of the elevatorcan be monitored as a precaution against the earth fault situationsdescribed above. The safety arrangement is implemented with the existingcomponents of the frequency converter in such a way that a monitoringprogram is recorded in the software of the control unit 6 of thefrequency converter, which program receives current measuring data fromthe current sensors 9A, 9B of the frequency converter and also receivesfrom the elevator control unit 8 information about the operating stateof the elevator and controls the IGBT transistors 14, 16 of the networkbridge 10 and of the motor bridge 12 of the frequency converter, on theone hand, for collecting information about an earth fault and, on theother hand, for bringing the motor drive 1 into a safe state when anearth fault is diagnosed. When an earth fault is diagnosed the controlunit 6 of the frequency converter sends information about the danger ofelectric shock relating to the earthed, accessible parts 3A, 3B, 3C, 3D,3E of the motor drive to the control unit 8 of the elevator, which sendsthe information onwards to the servicing center 9 for the elevators,e.g. via a wireless connection, an Internet connection or some othersuch suitable remote connection. In the following the operation of theaforementioned safety arrangement will be described in more detail.

The control unit 6 of the frequency converter receives from the elevatorcontrol unit 8 information about the operating state of the elevator,i.e. inter alia whether the elevator is driving or whether the elevatorcar is standing empty waiting for passengers. The software of thecontrol unit 6 of the frequency converter comprises differentdetermination methods for determining an earth fault when driving withthe elevator than during a standstill of the elevator.

An earth fault occurring in the output circuit 2B of the frequencyconverter, i.e. in a subcircuit of the main circuit 2 continuing fromthe motor bridge 12 to the electric motor 7, is determined during astandstill of the elevator by connecting the IGBT transistors of themotor bridge 12 that connect to the positive + busbar of thedirect-current intermediate circuit 11, or alternatively by connectingthe IGBT transistors of the motor bridge 12 that connect to the negative− busbar of the direct-current intermediate circuit 11, one at a time tobe conductive and by measuring with the current sensors 9B the currentflowing in the output circuit 2B. Current starts to flow if the outputcircuit 2B connects to an earth fault, e.g. as a consequence of damageof the winding insulations of the motor or as a consequence of aninsulation failure of the supply cables of the motor. Current does notflow at all or the current is extremely small if there is no earth faultin the output circuit 2B. A threshold value K1 is recorded in the memoryof the control unit 6 of the frequency converter, to which thresholdvalue the measured current is compared, and the control unit 6 diagnosesthat an earth fault has occurred if the current measured from the outputcircuit 2B of the frequency converter exceeds the threshold value K1.

An earth fault in the output circuit 2B of the frequency converter canalso be determined during a run with the elevator. In this case the IGBTtransistors of the motor bridge 12 that connect to the positive busbarof the direct-current intermediate circuit 11, or alternatively the IGBTtransistors that connect to the negative busbar of the direct-currentintermediate circuit 11, are connected to be simultaneously conductive,in which case the supply leads of the motor receive zero voltage. Thecurrent flowing in the output circuit 2B is measured with the currentsensors 9B, and if a change in the current exceeds the threshold valueK2 recorded in the control unit 6 of the frequency converter, thecontrol unit 6 diagnoses that an earth fault has occurred. Thedetermination method for an earth fault presented is suited to the motordrive according to FIG. 1, in which the output circuit 2B comprisescurrent sensors 9B in only two of the three different phases of themotor 7. If there were separate current sensors in all three phases, anearth fault could also be determined from the resultant of the measuredcurrents, i.e. from the length of the sum vector of the current vectors:an earth fault is diagnosed in the output circuit if the aforementionedresultant of the currents exceeds a certain threshold value.

The threshold value K1 is smaller than the threshold value K2 for thereason, among others, that the interference level of the main circuit 2during a standstill of the elevator is smaller than when driving withthe elevator, so that an earth fault can also be determined with asmaller threshold value k1 for current during a standstill of theelevator than when driving with the elevator (threshold value K2). Asmall threshold value K1 for current facilitates the diagnosing of anelectric shock hazard particularly in those motor drives 1 in which theearth fault current is small owing to, inter alia, the high impedance 21of the earth fault conductor 5.

Instead of measurement of the current, an earth fault of the outputcircuit 2B could in some cases also be determined by measuring thevoltage of the direct-current intermediate circuit 11, more particularlyif a large impedance, such as a charging resistor for the intermediatecircuit capacitors, is in series on the supply side of the frequencyconverter. In this case an earth fault in the output circuit 2B causesthe intermediate circuit voltage to drop.

When the control unit 6 of the frequency converter diagnoses that anearth fault has occurred, the control unit 6 sends information about theelectric shock hazard to the elevator control unit 8, from where it issent onwards to the servicing center 9 for the elevators, as statedabove. The elevator control unit 8 also removes the elevator from use,recording the drive prevention regulation in non-volatile memory, andafter this use of the elevator is prevented on the basis of the driveprevention regulation recorded in memory. In the same context thecontrol unit 6 of the frequency converter disconnects the current flowin the output circuit 2B by opening the IGBT transistors of the motorbridge, in which case the output circuit 2B and the earthed conductingpart 3B, 3C in earth fault are de-energized.

An earth fault occurring in the internal circuit 2A of the frequencyconverter, i.e. in a subcircuit of the main circuit 2 continuing fromthe motor bridge 12 via the direct-current intermediate circuit 11 andthe network bridge 10 to the current sensors 9A of the input side, isdetermined by measuring the currents flowing in the supply conductors ofthe network bridge 10 with the current sensors 9A and also bycalculating the resultant of the measured currents, i.e. the length ofthe sum vector of the current vectors, in the control unit 6 of thefrequency converter. A threshold value K3 is recorded in the memory ofthe control unit 6 of the frequency converter, to which threshold valuethe calculated resultant of the currents is compared, and the controlunit 6 diagnoses that an earth fault has occurred if the calculatedresultant of the currents (which is proportional to the magnitude of theground leakage current) exceeds the aforementioned threshold value. Thethreshold value K3 of the resultant of the currents is selected to be sosmall that an earth fault is detected even though the impedance 21 ofthe earthing conductor 5 were to limit the ground leakage current.

If the motor drive 1 of the elevator can be isolated with a contactorfrom the supply panel 15, the motor drive can be completely de-energizedby opening the contacts of the contactor after an earth fault isdiagnosed. In the embodiment of FIG. 1 the motor drive 1 of the elevatoris, however, implemented without contactors, in which case, when anearth fault is diagnosed, the motor drive is completely de-energized byconnecting the IGBT transistors of the network bridge 10 to besimultaneously conductive, in which case the supply conductors connectinto short-circuit, the fuses 18 in the supply board 15 burn out and thecurrent supply to the motor drive 1 disconnects. Instead of a fuse, alsoe.g. a line protection breaker or an automatic fuse could be used as ashort-circuit protective device 18.

The control unit 6 also sends information about the electric shockhazard to the elevator control unit 8, from where it is sent onwards tothe servicing center 9 for the elevators, as stated above. The elevatorcontrol unit 8 also removes the elevator from use, recording the driveprevention regulation in non-volatile memory, and after this use of theelevator is prevented on the basis of the drive prevention regulationrecorded in memory.

Taking the elevator into use again requires that a serviceman resetsfrom a manual user interface of the elevator control unit 8 the driveprevention regulation to off on his/her visit to the elevator.

In some embodiments the electric shock warning sent by the control unit6 of the frequency converter also contains information as to whether anearth fault has occurred in the internal circuit 2A of the frequencyconverter or in the output circuit 2B of the frequency converter. Theinformation can be transmitted to a servicing center 8, and it can beused to facilitate fault repair.

The invention is described above by the aid of a few examples of itsembodiment. It is obvious to the person skilled in the art that theinvention is not only limited to the embodiments described above, butthat many other applications are possible within the scope of theinventive concept defined by the claims.

The invention claimed is:
 1. A safety arrangement of an elevator,comprising a motor drive of the elevator, the motor drive comprising: amain circuit; an accessible conducting part, which is earthed; aninsulator, which is adapted to electrically insulate the conducting partfrom the main circuit; and a monitoring circuit configured to determinean earth fault of the main circuit, wherein in response to the earthfault being determined, the monitoring circuit forms a signal indicatingdanger of electric shock in the motor drive of the elevator, wherein thesafety arrangement is configured to form the signal indicating thedanger of electric shock in the motor drive both when driving with theelevator and during standstill of the elevator, and wherein themonitoring circuit is configured to use a different determination methodwhen driving with the elevator than during standstill of the elevatorfor determining the earth fault.
 2. The safety arrangement according toclaim 1, wherein the monitoring circuit is configured to determineground leakage current of the conducting part, and wherein themonitoring circuit is configured to determine the earth fault of themain circuit on the basis of the ground leakage current of theconducting part.
 3. The safety arrangement according to claim 2,wherein: the conducting part is earthed with an earthing mechanism; themonitoring circuit comprises memory, a threshold value of the groundleakage current of the conducting part being recorded in the memory; thethreshold value is determined in an earth fault situation from amagnitude of the ground leakage current flowing via the earthingmechanism, and the monitoring circuit is configured to determine theearth fault in the main circuit when the ground leakage current of theconducting part exceeds the threshold value.
 4. The safety arrangementaccording to claim 1, wherein: the main circuit of the motor drive ofthe elevator is formed from at least two subcircuits; and the insulatoris adapted to electrically isolate one or more of the subcircuits fromthe conducting part of the motor drive of the elevator.
 5. The safetyarrangement according to claim 4, wherein: one or more of thesubcircuits to be electrically insulated from the conducting part of themotor drive is/are connected to at least one second subcircuit with oneor more controllable electronic switches, a control pole of the one ormore controllable electronic switch being connected to the monitoringcircuit, and the monitoring circuit is configured by connecting theelectronic switch/electronic switches to determine an earth fault of theone or more subcircuits to be electrically insulated from the conductingpart occurring via the conducting part.
 6. The safety arrangementaccording to claim 1, wherein: the motor drive of the elevator comprisesan electric motor and a frequency converter, with which the electricmotor is controlled, and the frequency converter comprises a networkbridge to be connected to a power source, a motor bridge to be connectedto the electric motor, and a direct-current intermediate circuitconnecting the network bridge and the motor bridge.
 7. The safetyarrangement according to claim 6, wherein: the motor bridge comprisescontrollable electronic switches for supplying electric power from thedirect-current intermediate circuit to the electric motor, when drivingwith the electric motor and also from the electric motor to thedirect-current intermediate circuit when braking with the electricmotor, the insulator is adapted to electrically insulate the conductingpart of the motor drive of the elevator from an output circuit of thefrequency converter, the frequency converter being formed from asubcircuit of the main circuit of the motor drive continuing from themotor bridge to the electric motor, and the monitoring circuit isconfigured to determine an earth fault of the output circuit of thefrequency converter by connecting the electronic switches of the motorbridge with a switching instruction according to the determinationmethod for an earth fault.
 8. The safety arrangement according to claim1, wherein: a disconnection is fitted in connection with the monitoringcircuit for disconnecting current in the main circuit of the motor driveof the elevator, and the monitoring circuit is configured to disconnectthe current in the main circuit when an earth fault is diagnosed.
 9. Thesafety arrangement according to claim 8, wherein: the motor drive of theelevator further comprises an electric motor and a frequency converter,the frequency converter comprises an internal circuit, a network bridgeto be connected to a power source, a motor bridge to be connected to theelectric motor, and a direct-current intermediate circuit connecting thenetwork bridge and the motor bridge, the insulator is adapted toelectrically insulate the conducting part of the motor drive from theinternal circuit of the frequency converter, the frequency converterbeing formed from a subcircuit of the main circuit of the motor drivecontinuing from the motor bridge via the direct-current intermediatecircuit and network bridge to supply conductors of the power source, themonitoring circuit is configured to determine an earth fault of theinternal circuit of the frequency converter, and the monitoring circuitis configured to, when it determines an earth fault in the internalcircuit, disconnect an electricity supply from the power source to theinternal circuit of the frequency converter.
 10. The safety arrangementaccording to claim 9, wherein the monitoring circuit is configured todetermine the earth fault by measuring a voltage of the direct-currentintermediate circuit, and wherein the monitoring circuit is configuredto when it diagnoses the earth fault in the internal circuit, disconnectthe electricity supply from the power source to the internal circuit ofthe frequency converter.
 11. The safety arrangement according to claim9, wherein: the network bridge comprises controllable electronicswitches for supplying electric power between the power source and thedirect-current intermediate circuit, the safety arrangement comprises ashort-circuit protective device, which is fitted in series between thepower source and the network bridge, and the monitoring circuit isconfigured to disconnect the electricity supply from the power source tothe internal circuit by tripping the short-circuit protective device bycontrolling the electronic switches in different phases of the networkbridge to be simultaneously conductive.
 12. The safety arrangementaccording to claim 1, wherein: the monitoring circuit further comprisesa power meter for measuring power entering the main circuit of the motordrive and power leaving the main circuit, and the monitoring circuit isconfigured to determine an earth fault of the main circuit of the motordrive of the elevator occurring via the conducting part of the motordrive of the elevator from a difference between power coming into themain circuit and power leaving the main circuit.
 13. An elevator system,comprising: a motor drive for driving an elevator car of an elevator,the motor drive comprising an insulator; and a safety arrangement formonitoring electrical safety of the elevator, the safety arrangementcomprising: a main circuit; an accessible conducting part, which isearthed, wherein the insulator is adapted to electrically insulate theconducting part from the main circuit; a monitoring circuit, which isconfigured to determine an earth fault of the main circuit, wherein inresponse to the earth fault being determined, the monitoring circuitforms a signal indicating danger of electric shock in the motor drive ofthe elevator, wherein the monitoring circuit is configured to use adifferent determination method when driving with the elevator thanduring a standstill of the elevator for determining the earth fault; anda drive prevention apparatus connected to the monitoring circuit, thedrive prevention apparatus is configured to remove the elevator from usewhen the earth fault is determined.
 14. The elevator system according toclaim 13, wherein the elevator system is configured to send the signalindicating the danger of electric shock in the motor drive to aservicing center via a remote connection.
 15. The elevator systemaccording to claim 13, wherein: the elevator system is installed in anelevator hoistway and comprises a supply panel and is provided without amachine room; the supply panel of the elevator system is disposedoutside the elevator hoistway, and the motor drive of the elevator isdisposed in the elevator hoistway.
 16. The elevator system according toclaim 15, wherein the conducting part of the motor drive is earthed withearth electrodes only in the supply panel of the elevator system.
 17. Amethod for monitoring electrical safety in the elevator system of claim13, comprising the steps of: earthing the accessible conducting part ofthe motor drive of the elevator with an earthing mechanism; electricallyinsulating the conducting part from the main circuit of the motor driveof the elevator with an insulator; determining the earth fault of themain circuit from a ground leakage current of the conducting part of themain circuit; and in response to the earth fault being determined,forming a signal indicating the danger of electric shock in the motordrive.
 18. The elevator system according to claim 13, wherein the motordrive of the elevator comprises an electric motor and a frequencyconverter, wherein the frequency converter controls the electric motor,wherein the frequency converter comprises a network bridge connected toa power source, a motor bridge connected to the electric motor, and adirect-current intermediate circuit connecting the network bridge andthe motor bridge, wherein the monitoring circuit is configured todetermine the earth fault by measuring a voltage of the direct-currentintermediate circuit, and wherein the monitoring circuit is configuredto, determines an earth fault in an internal circuit of the frequencyconverter, disconnect an electricity supply from the power source to theinternal circuit of the frequency converter.